MPI_Init_thread(3): update refs about MPI_THREAD_MULTIPLE

Thanks to Andreas Lösel for bringing the outdated docs to our
attention.

Signed-off-by: Jeff Squyres <[email protected]>
(cherry picked from commit 0a52936)

Author: jsquyres

ompi/mpi/man/man3/MPI_Init_thread.3in

@@ -1,7 +1,8 @@
 .\" -*- nroff -*-
 .\" Copyright 2006-2008 Sun Microsystems, Inc.
 .\" Copyright (c) 1996 Thinking Machines Corporation
-.\" Copyright (c) 2010-2015 Cisco Systems, Inc.  All rights reserved.
+.\" Copyright (c) 2010-2020 Cisco Systems, Inc.  All rights reserved.
+.\" Copyright (c) 2020      Google, LLC. All rights reserved.
 .\" $COPYRIGHT$
 .TH MPI_Init_thread 3 "#OMPI_DATE#" "#PACKAGE_VERSION#" "#PACKAGE_NAME#"
 .
@@ -135,52 +136,27 @@ opening files, reading standard input, or writing to standard output.
 .
 .SH MPI_THREAD_MULTIPLE Support
 .
-MPI_THREAD_MULTIPLE support is included if Open MPI was configured
-with the --enable-mpi-thread-multiple configure switch.  You can check the
+MPI_THREAD_MULTIPLE support is included if the environment in which
+Open MPI was built supports threading.  You can check the
 output of
 .BR ompi_info (1)
 to see if Open MPI has MPI_THREAD_MULTIPLE support:
 .
 .PP
 .nf
-shell$ ompi_info | grep -i thread
-          Thread support: posix (mpi: yes, progress: no)
+shell$ ompi_info | grep "Thread support"
+          Thread support: posix (MPI_THREAD_MULTIPLE: yes, OPAL support: yes, OMPI progress: no, Event lib: yes)
 shell$
 .fi
 .
 .PP
-The "mpi: yes" portion of the above output indicates that Open MPI was
-compiled with MPI_THREAD_MULTIPLE support.
+The "MPI_THREAD_MULTIPLE: yes" portion of the above output indicates
+that Open MPI was compiled with MPI_THREAD_MULTIPLE support.
 .
 .PP
-Note that MPI_THREAD_MULTIPLE support is only lightly tested.  It
-likely does not work for thread-intensive applications.  Also note
-that
-.I only
-the MPI point-to-point communication functions for the BTL's listed
-below are considered thread safe.  Other support functions (e.g., MPI
-attributes) have not been certified as safe when simultaneously used
-by multiple threads.
-.
-.PP
-.nf
-    tcp
-    sm
-    mx
-    elan
-    self
-.fi
-.
-.PP
-Note that Open MPI's thread support is in a fairly early stage; the
-above devices are likely to
-.IR work ,
-but the latency is likely to be fairly high.  Specifically, efforts so
-far have concentrated on
-.IR correctness ,
-not
-.I performance
-(yet).
+Note that there is a small performance penalty for using
+MPI_THREAD_MULTIPLE support; latencies for short messages will be
+higher as compared to when using MPI_THREAD_SINGLE, for example.
 .
 .
 .SH ERRORS